Load strip for airplane wing and control surface covers



July 18, 1939. K scH T 2,166,182

LOAD STRIP FOR AIRPLANE WING AND CONTROL SURFACE COVERS Filed March 9, 1938 2 Sheets- Sheet 1 23 88 ao W W a e e e 9 e' e e e e e e e e e e e e e e a e e e e e e e e e e aa a? 'as' as a aa as to 26 ao m M w W INVENTOR ATTORNEY July 18, 1939. 2,l66,182

LOAD STRIP FOR AIRPLANE WING AND CONTROL SURFACE COVERS Filed March 9, 1938 2 Sheets-Sheet 2 INVENTOR BY KARL SCHMIDT mwz ATTORNEY Patented July 18, 1939 UNITED STATES PATENT OFFICE LOAD' STRIP FOR AIRPLANE WING AND CONTROL SURFACE COVERS 6 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) This invention relates to fastening devices for the covers of airplane wings and control surfaces and it has a particular relation to load-strips for securing the cloth or metal cover to the rib members of the wing frame structure.

Heretofore it has been` the practice to attach the fabric covering of an airplane wing to the capstrip of the rib member by a Iacing cord looped around the capstrip and cover and knotted at intervals. In this method the fabric cover is stretched over the airfoil frame in contiguous relation to the capstrips .of the rib members after which the usual reenforcing tape of a width equal to the capstrip is placed on the cover over the lb entire length of the capstrip and the two secured thereto' by the lacing cord which is looped tightly around the capstrip at intervals and tied.

In some instances the separate cord loops include both the top and the bottom capstrips of 20 the rib, and in other instances the cord loops lace the reenforcing tape and the cover to the upper capstrip only. After lacing in the manner described, the cover is protectively impregnated and in the finished state is both smooth and taut.

25 When this cover is subjected, in the air borne airplane, to a suction air load, that is, to the top cambered surface of the airfoil, the cover has a tendency to lift away from the capstrip at its points of attachment thereto due to the extensi- 3 bility of the lacing cord under load. The flight air load imposed on the cover varies constantly, depending not alone upon the atmospheric conditions but also upon the speed of the airplane and especially the rate of maneuvering the airplane.

35 Under normal flight conditions, the negative air load may be 8-45 1bs./sq. ft. and this may increase in value to approximately 300 1bs./sq. ft. When the airplane is sharply maneuvered at high velocity. Under these varying conditions, the

40 lacing cords are constantly changing length, corresponding to the load imposed on each cord. It will be readily understood that as the cover increasingly defiects, the loop of each lacing cord becomes more convergent at the point where it 45 loops over the fabric, with the result that the reenforcing tape is pinched together, thus allowing the lacing cord to bear against the side of the capstrip. This sawing action inevitably results in failure of the lacing cord, with the co further result that the safety of the airplane is seriously impaired. The lacing cord method of fabric cover attachment is therefore neither efiicient, durable, nor dependable.

Similarly, the Variable airloads described above 65 cause metal covers to constantly deflect in Varying amounts, with the result that fatigue failure is inevitable and may occur either in the sheet metal cover at the fastener, or in the fastener itself. The cover when variously loaded is subject to repeated stress fiuctuation, and this is 5 equally true of the rivet fastener which secures the metal skin to the capstrip.

It is therefore seen that the present methods of cover attachment are unsatisfactory, and in the case of a fabric cover the lacing cord is eX- o tensible and subject to severe abrasion, and in the case of the metal cover the high load concentration at the separate points of attachment to the capstrip invites early fatigue failure of cover or fastener.

The principal object of the present invention is to avoid the disadvantages hereinabove referred to by securing the cover to the wing by an improved loadstrip that eXtends the full length of the rib from its leading edge to its trailing edge and is secured to the capstrip at spaced intervals, the load-strip being substantially inflexible to resist bending between its points of loading.

With these and other objects in View, as well as other advantages that may be incident to the use of the improvements, the invention consists in the parts and combinations thereof hereinafter set forth and claimed, with the understanding that the several necessary elements constituting the same may be varied in proportion and arrangement without departing from the nature and scope of the invention, as defined in the appended claims.

In order to make the invention more clearly understood, there are shown in the accompanying drawings, means for carrying the invention into practical use, without limiting the improvements in their useful application to the particular construction, which, for the purpose of explanation, have been made the subject of illustration.

In the accompanying drawings:

Fig. 1 is a fragmentary plan View of an airplane wing having the covering thereof secured to the ribs by a load-strip embodying the present invention;

Fig. 2 is a Vertical transverse sectional View taken on line 2 2 of Fig. 1;

Fig. 3 is an enlarged fragmentary Vertical sectional View taken on line 3-3 of Fig. 2;

Fig. 4 is a fragmentary perspective View of a load-strip constructed in accordance with the invention;

Fig. 5 is a similar view of a slightly modified form of the load-strip shown in Fig. 4;

Fig. 6 is a similar view of another form of load-strip of hollow triangular cross-section; and

Fig. 7 is a similar view of still another form of load-strip of flattened tubular cross-section.

Referring to the drawings, an airplane Wing having an envelope or covering secured thereto in accordance with the invention is shown as comprising a rib In having front and rear longitudinal beams l I and '2 to which upper and lower capstrips |3 and M, respectively, are secured in any suitable manner. The capstrips l3 and '4 are also secured together by transverse bracing '5 so as to form a light but rigid structure. The upper capstrip '3 is preferably formed of a metal plate bent into the configuration shown in' Fig. 3 so as to form a hollow upper portion '6 of V- shape and a depending fiange I" of double thickness to which the bracing '5 is riveted. A washer plate or bar '8 is enclosed within the tubular portion '6 of the capstrip and is formed with drilled recesses at intervals.

In applying the covering a strip of fabric '9 is first secured to the upper surface and sides of the upper portion '6 of the capstrip '3 by airplane dope and the fabric covering 20 stretched over and fastened to the strip '9 by dope cement. A second fabric reenforcing strip 2| is next dope cemented to the fabric covering 20 and a load-strip 22 secured in position over the several layers of fabric by self-tapping screws 23 which engage the previously drilled openings in the cap and washer strips '3 and '8. The loadstrip 22 is preferably of substantially inverted T-shape in cross-section, being formed with a base portion 24 of a width corresponding to that of the portion [6 of the capstrip and with a vertical longitudinally extending rib or fiange 25 intermediate its width. The lower edges of the base portion 24 of the load-strip is preferably rounded, as indicated at 26, so as to minimize wear on the covering 20 and reenforcing strip 2| caused by the flexing thereof. The flange or rib 25 is also preferably recessed or milled at intervals to provide pockets 2" for the reception of the heads of the screws 23. A fabric sealing tape 28 is finally applied over the load-strip 22 and cemented to the covering 20 so as to fair the pockets 21, thus minimizing wind drag and the entire surface dope finished. It may be pointed out that the screws 23 are normally loaded in tension and there is little likelihood of them Working loose, but if this should occur the head of the screw will almost immediately bear against the sealing tape 28 suiciently to be detected. In actual practice the height of the rib or fiange 25 should be held to the minimum value consistent with the strength desired in order not to introduce undesirable wind drag.

In Fig. the load-strip 22 instead of being formed with recesses for the reception of the heads of the screws, as in the structure previously described, is formed with enlargements or swellings 29 at spaced intervals which are countersunk to receive fiat headed screws.

Fig. 6 illustrates another embodiment of the invention in which the loading strip is of hollow triangular cross-section and formed with a base 30 and upwardly converging sides 3'. These sides are cut away at intervals, as indicated at 32, to permit the round heads of the fastening screws 23 to bear directly against the base 30 and be disposed entirely within the geometrical boundaries of the load-strip.

Fig. 7 shows a load-strip of fiattened tubular construction having relatively fiat and wide base and upper portions 33 and 34 and relatively narrow curved side edges 35. In this form of the invention the upper portion 33 is recessed or countersunk to receive either round or flatheaded fastening screws.

Other mod'fications and changes in the proportions and arrangement of the parts, other than those shown, may be made by those skilled in the art, without departing from the nature and scope of the invention, as defined in the appended claims.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. Airplane wing construction comprising a capstrip having a fiat outer surface, a covering and a load-strip of substantially triangular crosssection, the base portion thereof being secured to the fiat surface of said capstrip to clamp the covering therebetween.

2. Airplane wing construction comprising a capstrip having a fiat outer surface, a covering and. a load-strip of substantially triangular crosssection, the base portion thereof being secured to the fiat surface of said capstrip to clamp the covering therebetween, and the converging sides thereof being recessed at intervals to receive the fastening devices.

3. Airplane wing construction comprising a capstrip having a fiat outer surface, a covering and a load-strip of substantially triangular crosssection, the base portion thereof being secured to the fiat surface of said capstrip to clamp the covering therebetween, said member having recessed enlargements of substantially semi-circular cross-section formed at intervals therealong for receiving the fastening devices.

4. Airplane wing construction comprising a capstrip having a fiat outer surface, a covering and a tubular load-strip of substantially triangular cross-section, the base portion thereof being secured to the fiat surface of said capstrip to clamp the covering therebetween.

5. Airplane wing construction comprising a capstrip having a fiat outer surface, a covering and a tubular load-strip of substantially triangular cross-section, the base portion thereof being secured to the fiat surface of said capstrip to clamp the covering therebetween, and the converging sides thereof being recessed at intervals to receive the fastening devices.

G. Airplane wing construction comprising a capstrip having a fiat outer surface, a covering and a load-strip of flattened tubular cross-section, the base portion thereof being secured to the fiat surface of said capstrip to clamp the covering therebetween.

KARL SCHMIDT. 

